2.6.6

Calculating the Relative Formula Mass

Test yourself

Calculating the Relative Formula Mass (Mr)

To calculate the relative formula mass of a compound, we need to know the relative atomic masses (Ar) of the elements that make the compound. Then we multiply the Ar values by the number of atoms of that element in the compound. Then we add these numbers together.

Illustrative background for E.g. hydrochloric acid (HCl)Illustrative background for E.g. hydrochloric acid (HCl) ?? "content

E.g. hydrochloric acid (HCl)

  • Identify the relative atomic mass (Ar) of each element in the compound:
    • Ar of hydrogen = 1
    • Ar of chlorine = 35.5
      • So, the total Mr of HCl is 1 + 35.5 = 36.5
Illustrative background for E.g. sulfuric acid (H<sub>2</sub>SO<sub>4</sub>)Illustrative background for E.g. sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) ?? "content

E.g. sulfuric acid (H2SO4)

  • Identify the relative atomic mass (Ar) of each element in the compound:
    • Ar of hydrogen = 1
    • Ar of sulfur = 32
    • Ar of oxygen = 16
      • So, the total Mr of H2SO4 is (2x1) + (1x32) + (4x16) = 98

Jump to other topics

1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

1.3Ecological Relationships & Classification

1.4Digestion & Nutrition

1.5Plants & Photosynthesis

1.6Biological Systems & Processes

2Chemistry

2.1Particles

2.2Chemical Reactions

2.3Atoms, Elements, Compounds

2.4The Periodic Table

2.5Materials & the Earth

2.6Reactivity

2.7Energetics

2.8Properties of Materials

3Physics

3.1Energy

3.2Forces & Motion

3.3Waves

3.4Electricity & Magnetism

3.5Matter

3.6Space Physics

4Disciplinary Knowledge

Unlock your full potential with Seneca Premium

  • Unlimited access to 10,000+ open-ended exam questions

  • Mini-mock exams based on your study history

  • Unlock 800+ premium courses & e-books

Get started with Seneca Premium